- **OpenFOAM Running, Solving & CFD**
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- - **PISO Question**
(*https://www.cfd-online.com/Forums/openfoam-solving/65986-piso-question.html*)

PISO QuestionHi Foamers,
A small question about the PISO algorithm implemented in icoFoam and other solvers. The fvVectorMatrix UEqn, defined for the momentum predictor is recalculated in each time step of PISO. Why are the coefficients of this matrix not set to zero before the new time step? Are all the values of this matrix recalculated and overwrited in the next time step. My problem is that I am trying to solve a problem where I have extra tensions besides the newtonian stresses, and I noticed that a PISO starts well but then it starts to miss behave, in particular giving a completely wrong velocity profile. Can be problem be attributted to problems in the calculation of the coefficient matrix or not? Can someone help me out? Titio |

Titio,
In C++, variables live only up to the next "}". So, UEqn is created in line 63 and deleted in line 106 of icoFoam.C. Henrik |

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